JERRY MCCREA/THE STAR-LEDGERJack Cohen, who researched gefilte fish and developed his own recipe for his bar mitzvah, enjoys the fruits of his labor at his ceremony earlier this month.

Beth Heinsohn, the descendant of Connecticut WASPs and an Episcopalian-turned-Jew by choice, is an ambitious home cook who raised an adventurous eater and budding chef in her son, Jack Cohen. So when Jack decided to research the history and cultural significance of gefilte fish, the traditional (and traditionally mocked) Jewish appetizer of poached fish balls, as part of his bar mitzvah preparation, she was game.

Together they pored over cookbooks, haunted fish markets, toted home bags of fish heads and bones and experimented with different kinds of fish, spices, herbs and fillers. Jack read Jewish folk tales, watched videos of elderly Jewish women making gefilte fish from scratch and even interviewed cookbook author Matthew Goodman ("Jewish Food: The World at the Table").

When Jack's great-aunt Marcia told him that her grandmother would buy a huge carp and let it swim around the upstairs bathtub a few days before Passover (presumably to get rid of the fish’s muddy taste), Jack’s eyes lit up. "I wanted to get a fish from Chinatown and let it live in the bathroom," he says.

That’s where his mother drew the line.

All told, they made variations of gefilte fish about a dozen times, eventually developing a boldly flavored version that they served at Jack’s bar mitzvah reception earlier this month. They recently whipped up another batch in the kitchen of their Jersey City townhouse. When asked whether they would be able to stomach more at Passover, which is prime gefilte time, Heinsohn laughed. "I’m kind of looking forward to it. Isn’t that weird?"

Gefilte fish is both the most beloved and reviled of Jewish appetizers. It looks like a desiccated gray sponge and often comes cloaked in a shuddering gelatin that can provoke likewise shudders at Sabbath and holiday dinners. The late ’60 radical Abbie Hoffman once recounted on film his attempt to serve gefilte fish to famed pediatrician and über-WASP Benjamin Spock: "I know he is not gonna eat it," Hoffman recalled in his own cramped kitchen, a pot of fish balls simmering on the stove. "Because if you’re not grown up in the culture and everything, if you haven’t had the gefilte fish, you’re not going to try it on your own."

Gefilte means stuffed, and the earliest versions date to the medieval times, when cooks would debone a carp, chop the flesh and add seasonings, then stuff it back inside the fish and poach it in fish stock. It wasn’t even originally a Jewish dish, says Joan Nathan, the celebrated cookbook author, but it became one because of the custom to eat fish on the Sabbath (the Talmud instructs men to make love to their wives on Friday nights, and fish is considered a symbol of fertility).

Eventually the step of stuffing meat inside the fish was discarded, and in Eastern Europe, when fish wasn’t easily available in the winter, the use of the fillers such as matzo meal, bread, eggs and onions allowed cooks to feed more diners.

Today, gefilte fish is usually bought canned or frozen: New Jersey-based Manischewitz packs 2 million pounds of fish each year for its several varieties, and ready-to-poach gefilte fish loaves are available in many supermarkets. "As it came across the ocean," Nathan says, "people got a little lazy."

There are two main strains of gefilte fish, the sweet and the savory, and a doctoral dissertation by a now-renowned Yiddish language professor identified a north-south boundary east of Warsaw that has come to be known as the gefilte fish line: The Polish Jews to the west preferred theirs sweet, and the Litvaks and Ukrainians on the east side liked theirs with lots of salt and pepper. Some enjoy gefilte fish robed in gelatin, while others, it is not too much of an exaggeration to say, would sooner eat their own intestines.

But almost all cooks, it seems, accessorize their gefilte fish with what Cohen calls a carrot hat. Any Jewish cookbook worth its kosher salt will include at least one recipe for gefilte, and a few authors have attempted to dress up — or disguise — what is essentially a fish meatloaf with exotic flavors (Goodman fries his in a spicy tomato sauce) or fancy styling (Susie Fishbein layers plain loaves and salmon loaves and garnishes the finished product with cucumber slices). Nathan includes a recipe for gefilte fish-stuffed cabbage in her new book, "Quiches, Kugels, and Couscous: My Search for Jewish Cooking in France."

ADENA STEVENS/FOR THE STAR-LEDGERCohen ladles his gefilte fish balls onto a platter in his Jersey City kitchen.

The gefilte fish Jack and his mother developed is much lighter in texture than the jarred version and bright with pickled lemon and fresh thyme.

After much experimentation, he settled on a mixture of tilapia and haddock, but salmon, cod and halibut are fine too, he says, so long as it’s reasonably priced. "If it’s going to be a lot of money, you might as well get the Manischewitz."

Jack, who belongs to the City Congregation for Humanistic Judaism in Manhattan, which emphasizes Jewish culture, heritage and values, delivered his findings, cheekily titled "Holy Carp: Gefilte Fish, Judaism and Me," at his bar mitzvah Oct. 2, and offered up bite-size gefilte fish balls afterward to great acclaim.

Jack "understood that this was much bigger than just a matter of recipes, that this was about the different way food is spread and evolves from one generation to the next," says Rabbi Peter H. Schweitzer. "Tradition is not about just repeating the safe things the way it was always done. The very fact of innovation is a part of our tradition."